What Are the Causes of Apple Leaf Scorching?
When the leaves of an apple tree look as if they have been burned, it could be a condition known as apple leaf scorch. Leaf scorch is a condition that interferes with the balance of water input and output in a plant. It causes leaves to become dehydrated, and they often die and drop to the ground. Mineral deficiencies and several chemicals, both organic and synthetic, can cause apple leaf scorch.
Apple trees that receive an insufficient amount of potassium, either in the soil where they grow or in the fertilizer you give them, can develop a scorched appearance. Leaves appear blue-green with yellowing on their edges and between their veins. Later in the progression of this condition, the edges of leaves become scorched and turn either gray-brown or brown.
Commercial apple growers use sprays that contain calcium nitrate to control a condition of fruit called bitter pit, according to the International Society for Horticultural Science. But it can cause leaf scorch, so alternatives have been studied in South Africa. Results of a program that used another calcium carrier called Calimax showed that Golden Delicious and Granny Smith apple trees did not develop leaf scorch.
Copper sulfate is an organic fungicide used to control certain fungal diseases of apple trees. Although it has been shown to be effective in controlling many apple diseases, it also can cause damage to the leaves and sometimes the fruit. It kills all types of plant tissues, according to West Virginia University. This undesirable trait has caused many growers to abandon copper sulfate in favor of synthetic fungicides.
The margins of apple leaves can develop a scorched appearance when the tree is subjected to hydrogen cyanamide, a chemical used for apple fruit thinning. It is marketed under the brand name Dormex. Large commercial apple growers, and those who grow other fruit such as plums, use this chemical to cause the necessary reduction in fruit that trees produce in order to save on the high costs of labor that would be involved to manually thin the fruit.